Mineral-insulated cable connector



April 5, 1966 F. B. STARK ETAL 3,244,796

MINERAL-INSULATED CABLE CONNECTOR Filed Sept. 12, 1965 Sheets-Sheet l 2is: W

INVENTORS r/m/m a 577%? flan 4.40 6. 1400/6 19 7' TOR/YE Y5 April 5,1966 F. B. STARK ETAL MINERAL-INSULATED CABLE CONNECTOR 2 BMW 1 054 e T.m W56 w WW W 5 Filed Sept. 12, 1963 14 T TOR/V5 Y5 United States Patent3,244,796 MINERAL-INSULATED CABLE CONNECTOR Frank B. Stark, Harrisburg,and Ronald C. Laudig, Camp Hill, Pa., assignors to AMP Incorporated,

Harrisburg, Pa.

Filed Sept. 12, 1963, Ser. No. 308,567 Claims. (Cl. 174-77) Thisinvention relates generally to electrical connectors, and in particularto electrical fittings for terminating and sealing the ends ofmetal-sheathed mineral-insulated cables.

The expression mineral-insulated cable, as used herein, denotes a typeof electrical cable or conduit comprising a seamless tubular metallicsheath, usually copper, which houses one or more conductors, the latterbeing maintained in a spaced insulated relationship to each other and tothe sheath by an especially electrically inert refractory mineralsubstance, such as powdered magnesium oxide. This type of cable is notonly highly resistant to moisture and various fluids, but is also highlyresistant to the effects of temperature changes.

These properties make this type of cable highly desirable for use underhazardous, corrosive, highly damp, or other conditions where itsparticular properties can be particularly utilized, e.g. in chemicalplants or on board ships. Unfortunately this type of cable is veryexpensive relative to ordinary wiring, and most previous terminatingconnectors for this type of cable required extensive stripping back ofthe outer copper sheath and removal of the mineral-insulation to exposethe conductors to serve as leads from the point of termination in to theswitch on other apparatus which is within the cable box. The advantagesof this type of cable are best realized when fluid tight fittings areused to terminate it to cable boxes, so prior connectors often wereforced to use cumbersome potting procedures to effect tightly sealedfittings.

Consequently, it is an object of this invention to provide an electricalconnector for mineral-insulated metalsheathed cable which requires onlya minimal amount of insulation stripping to effect the termination, andadvantageously this invention replaces the long bared cable conductorsby inexpensive leads securely spliced thereto.

Another object is to provide such a connector which simply andeffectively seals out fluids, e.g. moisture and combustible gases, fromthe mineral insulation and especially from the conductors therein, whichalso is tem perature resistant, and which resiliently supports the leadsexiting from said connector against unduly localized and harmfulflexing.

Still another object is to provide a termination connector which issimply and quickly applied without any potting and yet results in astrong, well-sealed connection.

Another advantage is that this connector is able to be easily andquickly applied, requires for application only tools which are readilyavailable and are of the type normally found in an electricians kit,that it may come substantially preassembled ready for application, thatit may provide a grounding path for the, cable sheath, and that it isreadily adaptable to various use requirements.

Other objects and attainments of the present invention will becomeapparent to those skilled in the art upon a reading of the followingdetailed description when taken in conjunction with the drawings inwhich there "ice is shown and described a preferred embodiment of theinvention; it is to be understood, however, that this embodiment is notintended to be exhaustive nor limiting of the invention, but is givenfor purposes of illustration in order that others skilled in the art maymore fully understand the invention and the principles thereof and themanner of applying it in practical use so that they may modify it invarious forms, each as may be best suited to the conditions of aparticular use.

In the drawings:

FIGURE 1 is a perspective view of our preferred embodiment, partiallyinstalled;

FIGURE 2 is an enlarged longitudinal section of the terminatingconnector of FIGURE 1, aligned as it should appear just prior to actualassembly to the prepared cable end;

FIGURE 3 is a partially sectioned longitudinal view similar to FIG. 2,showing the connector partially applied with the anti-burr bushing inplace and with the leads spliced to the cables conductors;

FIGURE 4 is a view generally similar to FIGURE 3, but showing thecompleted connector prior to installation; and FIGURE 5 is a viewgenerally similar to FIGURE 4, showing the completely installedconnection within its protective collar afiixed therethrough to a cablebox.

The preferred embodiment of the present invention as shown in FIGURES 1to 5 is a terminating connector 10 for separately splicing leads 12 tocorresponding conductors 14 of a mineral-insulated metal-sheathed cable16 while sealing the end of cable and insulating the resulting splices.

As shown in FIGURE 2, in the preferred embodiment the terminatingconnector 10 includes the subcombination 17 of a resilient insulatingspacer 18 with an outer shell 20 and with leads 12 threaded throughlongitudinal passages 24 therein, which leads 12 are advantageouslyvinyl insulated (according to common practice) and are eachcrimp-terminated beyond the neck portion 26 of shell 20 with a brassbutt splice connector 28. This subcombination 17 is generally suppliedto the customer in pre assembled form as illustrated at the right inFIGURE 2, together with a brass protective support collar 30, asplit-ring wedge 32, and cap nut 34. As an added builtin safety featurea ceramic bushing 37 is included being shaped to force the customerduring installation to expose and remove any conductive burrs resultingfrom stripping back the metal sheathing 36 which might otherwise cause ashort between the conductors 14 and the sheathing 36.

In the preferred embodiment the application of the terminating connector10 can best be described by the following example. First, the cable 16is prepared by stripping back enough of the metal sheathing 36 and themineral insulation 38 to expose a length of the solid copper conductors14 sufi'icient to fit into the splice connectors 28. See FIGURE 2. Thisstripping back must be far enough to permit access of a crimping tool tothe splice connectors 28. If the anti-burr bushing 37 is to be used,then the mineral insulation 38 should be removed from under the mineralsheathing 36 to a depth sufiicient to expose any potentially shortingmetallic burrs which result from cutting the sheathing, thus enablingthese burrs to he removed. For example, in a quarterof-an-inchmineral-sheathed cable the metal sheathing 36 would be stripped backabout one-half inch and the mineral insulation 38 would be furtherremoved from under the remaining sheathing to a depth of about an eighthof an inch as ilustrated in FIGURE 2. Second, with the cap nut 34, thesplit-ring wedge 32 and the collar 39 having been slipped onto the cableover a prepared end, oriented as illustrated in FIGURE 2, and with theceramic bushing 37 pushed over the bared conductors 14 and pressed intothe void left after the removal of the mineral insulation; thereafter,the splice connectors 28 are slipped over and securely crinrped to thesebared conductors 14, as shown in FIGURE 3. Next, the shell 20 containingthe resilent insulated spacer 18 is slid along the nowspliced leads 22until the neck portion 26 of theshell 20 has been snugly positioned overthe bushing 37 and the end of cable 16, with" the leading face oftheresilient spacer 1 3 butted up against bushing- 37 and with the splicescompletely encased within the longitudinal passages 24 of spacer 18.With the sub-assembly 17 in this position, a double O-cri-mp is appliedto the necl' portion 26 sealingly to gripthe shell 20 and the parcarried therein to cable 16. Anotherdoiible O cri'ni p 1 a lied to thebody portion 400i the shell 20 forcrbly'to s the resilient spacer 18against thebu'shing'M and around splices 29 thereby sealing the 6nd orthe Cable 16 and the splices 29. See FIGURE {1. Finally, as indicated bythe arrows in FIGURE 4,-- the brass collar 3'0 issli'd over thec'rimpe'd shell until it's shoulder 41 butts against the correspondingshoulder 43 of the-shell, the Wedge 32 is pushed up against the narrowend 45 of the'colla'r 30 to engage an inwardly sloping cam surface 42 onthe insidediameter ofthis narrow end portion 45-, anus then the cap nut34 is drawn over this wedge 32 and screwed onto the threaded end of thisnarrow portion: 45 forcing the wedge against the cam surface 42 andtherefore radially constricting this split-ringaround cable 1-6- untilthe split faces are drawn together into an air-"tight seal. anchoringthe collar 30 to cable 16. The broader end portion- 44' of the collar 30advantageously has a tapered self-sealing thread which is adapted to bescrewed' into an appropriate hole in the cable box 46. Asillust'rated'the central portion of this collar 30 is formed into a hexagonal nut tofacilitate screwing this collar ihto the cable box. Advantagcously' thiscollar 30' would be mounted on the cable box- 46 befofe the cap nut 34:and wedge 32 are applied to its other end.

The resilient insulating spacer 18 is shaped to" fit and be held snuglywithin the body portion 40 fv the shell- 20 and has longitudinalpassages 24 running through it which equal in number, and align withrespective conductors 14. These passages 24 are just large enough toaccommodate leads 12. This spacer 18 might well be made from anyelastomer having the propertiesset forth below. It has been found thatsilicone rubbers or neoprene rubber are particularly useful for thispurpose. The particular ones of the properties below which determinet-heelastorner chosen for the jobwill, of course, depend upon the ensvironment' in which it is to be used; If extreme heat conditions areanticipated then naturally a rubber which preserves its elasticitywithout deterioration in= spite of thigh temperatures will be highlydesirable.-- Furthermore, since this spacer 18 will be subjected tocrimping it is important that the elastomer employed should retain itsdesirable properties after powerful squeezing.- It is desirable that theelastomer used should-have a compression set of under 20% of theoriginal deflection. This will ensure that sufficient resiliency isretained by the spacer 18 after crimping to maintain an ifcctive seal.Related to this low compression set, i.e. resilient displacement withminimal permanent defo'rmati'om. is the ability of the material toresistcreep. If an eifective seal is to be maintained for an extendedperiod, the tendency of the material to creep should be minimal. Thereare available on the market special w compression setsilicon'e rubberswhich are recommended for use in the: tempera ture range of from -13()to +500 F. and even short 1 flashes of significantly higher temperaturesuch as might be encountered under hazardous conditions; When this iscombined with the added features of good moisture resistance, goodelectrical properties maintained over the entire operable temperaturerange, and good resistance to lubricating oils and hydraulic fluids; itcan be appreciated that these special low compression set siliconerubbers are highly desirable for use in the spacer 18. Examples ofcommercially available low compression set organopolysiloxane rubbersinclude: Dow Corning Corporations Silastic 8-2096 U, 8-2097 U, and S2098U, and General Electric Companys SIS-36 2, SE-372, SE+3701 and S-E-382.These silicone rubbers have the [following generalized formula: -(R SiOwhere the R-groups are" usually methyl, but in the low compression setsilicone rubbers these R-groups are reputed to have a. vinyl form whichencourages cross-linking in the actual polymer; The compression set testprocedures have been well standardized, see ASTM vD 39 5-55, Method B.The general requirements tor H-igh- Temperature Resistant and LowCompression Set silicone rubbers have been thoroughly set forth in themilitary specification: Mil. R. 84-7 D; Class II B; I p The shell 20 isadvantageously formed or a tube of r with one end rolled down to a neckportion 26 shoulder 48 and with the other end roll'e o-ve'r curvedfet'aining lip 48, the latter for gripping and tent fling the spacer 18between it and the shoulder 43 within the" body portion" 40 of thisshell 261- As indi= eaten" earlier the neck portion 26 has an insidediameter slightly larger than the outside diameter of the cable 1*6 toenable a sealing O-crim'p to be effected therebetween. The accessorifice 50 defined by lip 43 at the end oh the shell serves an importantfunction in permitting the contrpres'sion of the spacer 18 while beingc'rimped to remain withinthe safe lirn'its by acting as a safety valvesuch that any over-compression will be avoided by a: protrusion ofthe-elaston'ierout of the open end 50. This safety valve eifectimportant because it has been hound that. exc'essive compression ofelastomers generally reduces their expectancy severely, particularly atelevated temperatures Itis a well known fact that silicone rubber whencompletely sealed from the air will tend to revert tov powder or pasteat relatively low temperature elevations. Fr"- completely sealed at 300F., such reversion will result; while even slight ventilation willnorm-ally eliminate reversion up to 500 F. Thus, this access orificepermitsbreatlring necessary at high temperatures; For the foregoingreasons, the lip 48 should be' only just large enough to contain thespacer within the shell. Another advantage or having this opening 50 agenerous size is so that the leads 12, if subject to' substantialflexing, areresiliently supported by the spacer and are not subject tochafing against the metallic lip 48.

The spacer =l'8' should be sufliciently wide such that the compressiondue to crimping will not be excessive at the point. or crimp; This is toavoid spreading this dielectric too thin and to avoidlocalizeddeterioration resulting from excessive com ression as was mentionedabove This invention can be adapted for use with a tninerah insulatedcable having any number or conductors and with any size of such cable.Also the metal collar 3'0 may be constructed to conform to safetyspecifications to ensure an explosion-proof termination for use inhazardous conditions.

Changes in construction will occur to those skilled in the artandvar-ious apparently different modifications and embodiments may bemade without departing from the scope ofthe invention. The matter setforth in the foregoing description and accompanying drawings is offeredbyway of illustration only.- The actual scope of the invent-ionisintended tobe defined in the foliowingclaims when viewed in theirproper'perspective against the prior art.

having a generous access orifice at its opposite We claim:

1. A device for terminating at a cable box and the like, amineral-insulated metal-sheath cable having at least one conductor,which device comprises a lead for each conductor spliced onto a shortbared portion of the corresponding conductor, a resilient insulatingspacer individually enclosing, mechanically supporting, anddielectrically separating within longitudinal passages said splicedconnections from each other and any further adjacent conductingmaterial, a copper shell formed with a cylindrical neck portionextending back over said cable and sealingly crimped thereto and with acylindrical body portion having its free end cur bed inwardlysufli-cient to contain said resilient spacer Within said body portionwhile leaving a generous access orifice for said leads and tfurther saidbody portion being crimped to form the resilient spacer into anysubstantial remaining voids with the shell.

2. A device for terminating leads to a mineral-insulated metal-sheathcable having at least one conductor, which device comprises a resilientinsulating spacer having at least one passage therethrough, each suchpassage positioned to align with a respective conductor of said cableand shaped to enclose and insulate a splice made between one of saidleads and a bared end portion of the corresponding conductor; a shellhaving said spacer held therein and having means adapted to fix one endof said shell in a sealing relation to said cable, said shell furtherend, whereby crimping said shell with it positioned with said resilientspacer insulating around said splices and adjacent to said cable andwith it securely sealed to said cable forms the spacer into anysubstantial remaining voids within the shell.

3. A device as described in claim 2 wherein said resilient insulatingspacer is composed of a temperature and creep resistant rubber.

4. A device for terminating leads to a mineral-insulated metal sheathcable having at least one conductor, which device comprises a resilientinsulating spacer having at least one passage therethrough, each suchpassage positioned to align with a respective conductor of said cableand shaped to enclose and insulate a splice made between one of saidleads and a bared end portion of the corre sponding conductor; a shellformed with a neck portion being shaped to fit over said cable whereby acrimp applied thereto seals said shell to said cable and with a bodyportion containing said spacer therein and having its free end curvedinwardly sufficient to retain said spacer While leaving a generousaccess orifice, said body portion being adapted to receive a crimp aftersaid shell and its spacer have been positioned over leads crimped tosaid conductors and said shell has been securely crimped to said cablein order thereby to form the spacer into any substantial remaining voidswith the shell.

5. A device for terminating at a cable box and the like, amineral-insulated metal-sheath cable having at least one conductor,which device comprises a lead for each conductor spliced onto a shortbared portion of the corresponding conductor, a resilient insulatingspacer individually enclosing, mechanically supporting, anddielectrically separating within longitudinal passages said splicedconnections from each other and any further adjacent conductingmaterial, a copper shell formed with a cylindrical neck portionextending back over said cable and sealingly crimped thereto and with acylindrical body portion having its free end curved inwardly sufiicientto contain said resilient spacer within said body portion while leavinga generous access orifice for said leads and further said body portionbeing crimped to form the resilient spacer into any substantialremaining voids with the shell, having a portion of its conductorsstripped bare, additionally has some mineral insulation removed fromunder the metal-sheath of a predetermined depth suflicient to ensurethat any burr remaining after the stripping of the metal-sheath isexposed and removed, and a solid dielectric bushing having longitudinalpassages passing the bared conductors therethrough and spaced at leastto plug the void left by said removed mineral insulation and providing aface for said resilient spacer to butt up against.

6. A device for terminating a mineral-insulated metalsheath cable havingat least one conductor through a hole in a rigid metal member such as acontrol panel, cable boxes and the like which device comprises a leadfor each conductor spliced onto a short bared portion of thecorresponding conductor, a resilient insulating spacer individuallyenclosing, mechanically supporting, and dielectrically separating withinlongitudinal passages said spliced connections from each other and anyfurther adjacent conducting material, a copper shell formed with acylindrical neck portion extending back over said cable and sealinglycrimped thereto and with a cylindrical body portion having its free endcurved inwardly sufiicient to contain said resilient spacer within saidbody portion while leaving a generous access orifice for said leads andfurther said body portion being crimped to form the resilient spacerinto any substantial remaining voids with the shell, metal collar meansprotectively enclosing said crimped shell and secured to said rigidmetal member, and means anchoring said cable to said member through saidcollar means thereby to protect said splices from undue tensile strain.

7. A terminating device for mineral-insulated metalsheath cable havingat least one conductor which comprises an insulated lead for eachconductor, a splice connector crimped to one end of each lead wire withthe free end of the connector adapted to receive a crimp onto a shortbared portion of the corresponding conductor of the cable to beterminated, a resilient insulating spacer having longitudinal passagesfor accommodating said respective leads and adapted to slip over saidsplice connectors after the latter have been crimped to said baredconductors thereby to enclose and insulate the resulting splices, ashell formed with a neck portion adapted to accommodate said cable andto receive a sealing crimp onto said cable and with a body portionhaving its free end curved inwardly sufiicient to contain said resilientspacer within said body portion while leaving a generous access orificefor said leads, said body portion being adapted to receive a crimp aftersaid shell has been positioned with said resilient spacer insulatingaround said splices and adjacent to said cable and with its neck portionsecurely crimped to said cable in order thereby to form the spacer intoany substantial remaining voids within the shell said spacer beingpositioned within said shell and carrying said leads within itslongitudinal passages.

8. A device as described in claim '7 wherein said resilient insulatingspacer is composed of a rubber chosen from the group consisting ofsilicone rubber and neoprene rubber and which is temperature andmoisture resistant and has a compression set of less than 20% of theoriginal deflection.

9. A device for terminating at a cable box and the like, amineral-insulated metal-sheath cable having at least one conductor,which device comprises an insulated lead for each conductor, asolderless connector crimp-splicing each lead wire onto a short baredportion of the corresponding conductor, a resilient insulating spacerindividually enclosing, mechanically supporting, and dielectricallyseparating within longitudinal passages said splice connectors and anyattached bare wire from each other and any further adjacent conductingmaterial, a copper shell formed with a cylindrical neck portionextending back over said cable and sealingly crimped thereto and with acylindical body portion having its free end curved inwardly suflicientto contain said resilient spacer within said body portion while leavinga generous access orifice for said leads and further said body portionbeing crimped to form the re- 7 sili'enf spacer into any substantialremaining voids with the shell.

10. A device as described in claim 9 wherein said resilient insulatingspacer is composed of a rubber chosen from the group consisting ofsilicone rubber and neoprene rubber and which is temperature resistantand has a compression set of less than 20% of the original defiection.

Iieferences Cite d the Examiner UNITED STATES PATENTS Q iN AT M 11/1950(311661 31115111. 12/19 52 Great Qritairi. 11/1961 Great Britain.

RQBERT K. SCHAEFER, iri'hidzj 6x11511267.

LARAMIE E. ASKIN, Examiner. w. B. FREDRICKS, Assist dni Exdmini.

1. A DEVICE FOR TERMINATING AT A CABLE BOX AND THE LIKE, AMINERAL-INSULATED METAL-SHEATH CABLE HAVING AT LEAST ONE CONDUCTOR,WHICH DEVICE COMPRISES A LEAD FOR EACH CONDUCTOR SPLICED ONTO A SHORTBARED PORTION OF THE CORRESPONDING CONDUCTOR, A RESILIENT INSULATINGSPACER INDIVIDUALLY ENCLOSING, MECHANICALLY SUPPORTING, ANDDIELECTRICALLY SEPARATING WITHIN LONGITUDINAL PASSAGES SAID SPLICEDCONNECTIONS FROM EACH OTHER AND ANY FURTHER ADJACENT CONDUCTINGMATERIAL, A COPPER SHELL FORMED WITH A CYLINDRICAL NECK PORTIONEXTENDING BACK OVER SAID CABLE AND SEALINGLY CRIMPED THERETO AND WITH ACYLINDRICAL BODY PORTION HAVING ITS FREE END CURBED INWARDLY SUFFICIENTTO CONTAIN SAID RESILIENT SPACER WITHIN SAID BODY PORTION WHILE LEAVINGA GENEROUS ACCESS ORIFICE FOR SAID LEADS AND FURTHER SAID BODY PORTIONBEING CRIMPED TO FORM THE RESILIENT SPACER INTO ANY SUBSTANTIALREMAINING VOIDS WITH THE SHELL.